/*
 * Copyright 2010-2012 Susanta Tewari. <freecode4susant@users.sourceforge.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package bd.org.apache.commons.math.random;

/**
 * This class implements the WELL19937c pseudo-random number generator
 * from Fran&ccedil;ois Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
 * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
 * Pierre L'Ecuyer and Makoto Matsumoto <a
 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
 *
 * @version $Id: Well19937c.java 1244107 2012-02-14 16:17:55Z erans $
 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
 * @since 2.2
 */
public class Well19937c extends AbstractWell {

    /**
     * Serializable version identifier.
     */
    private static final long serialVersionUID = -7203498180754925124L;

    /**
     * Number of bits in the pool.
     */
    private static final int K = 19937;

    /**
     * First parameter of the algorithm.
     */
    private static final int M1 = 70;

    /**
     * Second parameter of the algorithm.
     */
    private static final int M2 = 179;

    /**
     * Third parameter of the algorithm.
     */
    private static final int M3 = 449;

    /**
     * Creates a new random number generator.
     * <p>The instance is initialized using the current time as the
     * seed.</p>
     */
    public Well19937c() {

        super(K, M1, M2, M3);
    }

    /**
     * Creates a new random number generator using a single int seed.
     *
     * @param seed the initial seed (32 bits integer)
     */
    public Well19937c(int seed) {

        super(K, M1, M2, M3, seed);
    }

    /**
     * Creates a new random number generator using an int array seed.
     *
     * @param seed the initial seed (32 bits integers array), if null
     * the seed of the generator will be related to the current time
     */
    public Well19937c(int[] seed) {

        super(K, M1, M2, M3, seed);
    }

    /**
     * Creates a new random number generator using a single long seed.
     *
     * @param seed the initial seed (64 bits integer)
     */
    public Well19937c(long seed) {

        super(K, M1, M2, M3, seed);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected int next(final int bits) {

        final int indexRm1 = iRm1[index];
        final int indexRm2 = iRm2[index];

        final int v0       = v[index];
        final int vM1      = v[i1[index]];
        final int vM2      = v[i2[index]];
        final int vM3      = v[i3[index]];

        final int z0       = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
        final int z1       = (v0 ^ (v0 << 25)) ^ (vM1 ^ (vM1 >>> 27));
        final int z2       = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
        final int z3       = z1 ^ z2;
        int       z4       = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));

        v[index]    = z3;
        v[indexRm1] = z4;
        v[indexRm2] &= 0x80000000;
        index       = indexRm1;


        // add Matsumoto-Kurita tempering
        // to get a maximally-equidistributed generator
        z4 = z4 ^ ((z4 << 7) & 0xe46e1700);
        z4 = z4 ^ ((z4 << 15) & 0x9b868000);

        return z4 >>> (32 - bits);

    }
}
